Do HVAC's get the hickups?

Do HVAC\'s get the hickups?

Both this winter and summer i have noticed some strange behavior from my HVAC unit. I have AC and gas heat. I set it for 68 in the winter and 72 in the summer. ANyway, about the middle of the night or early morning it will cycle off and on constantly. It makes it difficult to sleep and I just turn it off or set it to a new temperature. Its one of the older thermostats with just a spring and mercury bubble in it, not electronic.

Has anyone experienced this before? Should i do something differently?

Re: Do HVAC\'s get the hickups?

Its time for a new thermostat.

I'd recommend a programmable electronic one and you'll most likely lower your energy bill to boot! /ubbthreads/images/graemlins/wink.gif

Re: Do HVAC\'s get the hickups?

Most thermistats have something called heat anticipation. If your system cycles constantly, it is either broken, or set improperly. The newer programmable thermostats often figure out how the system behaves, and calculate an appropriate setting.

You can often get a fully programmable Honeywell unit on eBay for about $25. Just make sure you get one with a base that is compatible with your system. (millivolt, single stage, multi-stage, heat pump, gas, oil, mixed (gas heat/electric AC) all require different wiring configurations (and different bases on the thermostate to accomodate the various configurations).

Re: Do HVAC\'s get the hickups?

Its one of those basic rectangle units with a lever and two switches. One switch for heat or air and the other for the fan.

I had considered a programmable one, Ive seen them at walmart for 20 dollars or so. I am renting an apartment and would hate to put money into it. Even if i save some power for the AC in the summer, it would take a few years to get it back.

So, thats called heat anticipation? I do find it strange that regardless of the inside temp when its on ac, it takes a few minutes before it starts up. I cut my ac off and heat when I leave of a day. Unless its like below freezing out, I turn the heat down, but I cut the ac off when I leave as it makes my bill cheaper by 20 dollars a month.

Re: Do HVAC\'s get the hickups?

Probably worth investing in the thermostat anyway, just put the old one away and swap it back in when you move -- $25 is a small price to pay for sanity eh?

Re: Do HVAC\'s get the hickups?

if you're renting then they should fix it for you for free. Give them a call.

Because this is going to rapidly and I mean in not that many more days, burn out the compressor. You can't restart them when the system is still under pressure! Thats very bad for them. So whatever you do, do it soon. And they should do it for you as they are going to save a LOT of money by replacing a bad thermostat rather than the compressor! (and you'll be without AC a lot shorter time than if they have to negotiate the cheapest price for the lowest bidder to come in to your place to do a crappy job /ubbthreads/images/graemlins/smile.gif )

If you do opt to do it yourself, google the wiring diagrams and make sure you note the names of the wires as printed on the old thermostat and the colors of wire they attach to. Dont just assume that the colors are what they say in the book with the new thermostat. The last guy wiring your system might have been a maniac /ubbthreads/images/graemlins/smile.gif

Lastly, turn the circuit breaker off for the air handler, not just the compressor when you do it. If you accidently short the wires you'll blow the 24v transformer in the furnace and again you'll be waiting on the negotiation by your landlord to get the lowest bidder to come down in price and throw a fix together for you whenever they can get around to it.

EDIT: because I can't type after 10pm it seems...

Re: Do HVAC\'s get the hickups?

My place is rented. I kept the old thermostat (which I may put back when I leave), but even then, I have a time of day electric rate, and I figured out the $25 would be recovered in lower bills within a few months (that was 3 years ago). I also don't have to remember to turn off the heat or the AC, at 9AM when the rate goes up, the set point moves up considerable for AC, or down considerable for heat,
and moves back again about 9PM M-F. Weekends are considered off peak, so the system is set to allow me to sleep in on weekends (the thermostat has 4 'time' zones (sleep,get up, away, return), and can be set M-F, as well as either Sat-Sun as a pair, or as separate days.
Just program the temps for the times and the days of the week, and that's that.

On many systems, if they are actually OFF as opposed to being below the set point for heat pump/air conditioning, there is a delay of several minutes before startup. This is to give the heater in the oil a chance to warm the oil in the compressor. On some systems the heater on anytime the breaker is on, on other only if the system is turned on. on others it is a kind of 'anti-bounce' to prevent rapid cycling.

The challenge on these things isn't programmimng them, it is finding a unit that matches the wiring requirements of the system!

Re: Do HVAC\'s get the hickups?

I often encounter such problem like this with my A/C and I found out that when the louvers of the discharge air is pointing towards the air intake, the thermostat immedietly sensed the cold temp. and stop the compressor prematurely.This is a typical problem also known as "short cycling" and much more noticeable at the middle of the night or in the morning when the temp. is cold. The basic remedy for this is to divert the discharge air away from the intake louvers or if it is in "auto swing mode", just put it to steady mode with louvers pointing away to the air return..If the problem persist then "GO to" the above thermostat sugestions...

Re: Do HVAC\'s get the hickups?

One potential fly in the ointment... Heat pumps don't work with many of the programmable thermostats. If the house/building has a heat pump/AC unit, the thermostats for those can be more expensive.

Give the building maintenance folks a call, and mention that replacing the thermostat will be cheper than the compressor.

Re: Do HVAC\'s get the hickups?

probably what ledmania said, the thermostat is being assaulted with cool then shutting down prematurly.

like a computers cooling check the FLOW, i have seen so much reduculous stupidity in AC systems. like who is the idiot (ahh gee thats not being nice) that puts vents with 500CPF output in a room, then makes the door seal so well that about 10CPF can Squeeze out of the room to recycle back in to the intake?

Programable thermostats are great, but them old mercury switch things would last forever, and no batteries needed or stupid computers in them to make errors.

the cool thing about a GOOD programable is you can set the number of DEGREES that it cycles at, to reduce cycling from the thermostat being hit wrong.
but still again, most of the time its the SITUATION that its in, or that you put it in that makes the biggest differences.

Check your flows, analize where the air MUST have to go, where leaking air goes (open window, poorly sealed garage door etc) , and comes from, and where the vaccumes are (intake) and the blowers. what doors (and walls) it has to TRY and get through to get there.

Analize anything next to a thermostat that uses energy aka puts out heat, for what can cause it to go the other way. sombody puts a 350W HDTV under the thermostat , then wonders why the poor thing dont work right /ubbthreads/images/graemlins/smile.gif or the stereo, or whatever uses power, usually puts out heat, and heat convectionally flows upward. Gee its always nice and cool in here when the tvs on , mabey the tv makes the ac work better /ubbthreads/images/graemlins/crazy.gif

EX: change from short carpet to deep pile shag, and the air passage under a door becomes blocked from ability to flow. suddenly that 14seer AC is as efficient as any other pos you had put in /ubbthreads/images/graemlins/smile.gif

Re: Do HVAC\'s get the hickups?

Cobb, if your 'stat works normally at other times and only "short cycles" in the wee hours, I'd suspect a different problem. Are doors closed which are open during waking hours? Are there any other changes which affect airflow? Does this happen only when outside temps are very cool or very hot?

Re: Do HVAC\'s get the hickups?

Thanks for the suggestions. I may consider a digital thermostat and swap it out after flipping the breakers and researching the wiring diagram. Its a basic AC with gas heat on what looks like 110 volts. Its rather loud, like a hurricane when its on heat or ac. No unusual noises like a problem exist.

I did call the folks to fix it, but unless it acts up when they are here they wont fix it. I had a relay go bad that caused the fan to quit running when the ac or heat was on and cause the coils to ice up. It wasnt til I hit the wall while it was on and he saw the breaker arc that he replaced it.

no, no air vent near it or hdtv. Now it only happens at midnight to early morning. As a side note its not uncommon to have the fire alarm or CO2 detector to go off or a neighbors for what seems no reason. According to the local fire dp something funky is up with the vents to the hvac and when the wind blows a certain way it sets off the co2 and fire alarms.

I close off the bed room when I am here and its on. When away, I shut it off and open the doors.